Surfactants are molecularly dispersed in a dilute aqueous solution, but as the concentration of the surfactants in the solution increases, the surface tension of the solution decreases down to a point at which the surfactants in the solution form aggregates having inwardly oriented hydrophobic groups and outwardly oriented hydrophilic groups thereof. Such aggregates are called micelles and the concentration at which micelles are formed is called the critical micelle concentration (CMC). Physical properties of the surfactant solution, e.g., interfacial tension, surface tension, electrical conductivity, detergency and intensity suddenly change around the CMC.
Micelles in an aqueous surfactant solution are of a spherical shape having inwardly oriented hydrophobic hydrocarbon chains and outwardly extended hydrophilic head parts, while micelles in an oil solution have a reversed shape in which the hydrophobic parts are inwardly oriented and hydrophilic chains are outwardly extended.
Meanwhile, in the adsorptive separation of materials active carbon and silica gel are commonly used. The active carbon and silica gel adsorb materials through physical adsorption and they are generally disposed after use due to the difficulty of desorbing the adsorbed materials.
Recently, Steven R. Kline has found based on a small angle neutron scattering (SANS) experiment that the cylinderlic micelle structure of a specific surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB) having a polymerizable counter ion, is maintained by polymerization of the polymerizable counter ion and the polymerized micelles are structurally stable against the temperature change in an aqueous solution (Langmuir, 1999, 15, pp 2726-2732). It has also been shown that such micelle structure of the polymerized surfactant can be obtained regardless what kind of a polymerized counter ion is used. However, the polymerized CTVB has different solubilities in different solvents and it is soluble in an organic solvent such as methyl alcohol but not in water, showing that the polymerized micelles cannot always be maintained in the solid form. Surfactants having a micelle structure have been used in the preparation of a porous inorganic material. For example, U.S. Pat. No. 5,220,101 describes a synthesis of a porous inorganic crystalline material comprising the steps of conducting a condensation reaction between cetyltrimethylammonium hydroxide, NaAlO2 and SiO2, and calcinating the condensation mixture at 550° C. The resulting porous inorganic crystalline material selectively adsorbs hexane over water in a water/hexane mixture when the surface of the porous material is modified by an inorganic surface modifier, chlorotrimethylsilane. Such selective adsorption of the surface-modified porous material has nothing to do with the surfactant used, the surfactant only providing the material with porosity.